INHIBITORY EFFECTS OF SOY AND RYE DIETS ON THE DEVELOPMENT OF DUNNINGR3327 PROSTATE ADENOCARCINOMA IN RATS

METHODS. Dunning R3327 PAP prostate tumors were transplanted in 125 ra ts, the rats were divided into five groups, and tumor development was examined for 24 weeks during treatment with diets containing 33% of so y flour (SD), rye bran (RB), heat-treated rye bran (HRB), or rye endos perm (RE). RESULTS. In the SD, RE, and HRB groups, significantly fewer palpable tumors and lower tumor volume were detected 14 and 16 weeks after transplantation when compared with the control, fiber-free dieta ry (FF) group. The body weight was lower 16 weeks after tumor transpla ntation in the RE and HRB groups when compared with the control group (P < 0.05). Rats in the RE and the HRB groups had a significant lower energy intake than the FF group during the first metabolic observation period, 3-6 weeks after tumor transplantation (P < 0.05), whereas the energy intake was the same in all groups during the second metabolic observation period, 13-16 weeks after tumor transplantation However, w hen the tumor volume was adjusted for the body weight of the animals, there were still significant lower tumor volumes in the SD, RE, and HR B groups compared with the FF group (P < 0.05). A significant increase in daily urinary excretion of the isoflavonoids, daidzein, A desmethy langolensin, equol, and Genistein, was observed in the rats fed SD, an d of the ligands enterolactone and enterodiol in the rats fed RE and H RB during both metabolic periods. There were no differences in testost erone levels between the groups. CONCLUSIONS. The present study shows that SD inhibits implanted prostate cancer growth. Although RE and HRB had a protective effect, further studies are needed to exclude the po ssibility that a low energy intake played a role in this respect. The results suggest that phytoestrogens (isoflavonoids and ligands), may b e responsible for the delayed prostate tumor growth. Prostate 36:151-1 61, 1998. (C) 1998 Wiley-Liss, Inc.